Coupling and loading measurements for a dielectric-filled ICRF waveguide coupler

Experiments were carried out to verify models of the reflection coefficients and the phase transitions for matched or loaded dielectric-filled waveguide couplers in the ion cyclotron range of frequencies (ICRF). A model for the plasma load simulation in the waveguide is developed and examined permanently using the time-domain features of an HP.8510 network analyzer. The loss properties of deionized water, which was used for laboratory waveguide dielectric tests, are also discussed. Close agreement between the coupling models and measurements is noted. For a matched coupler, the optimal power-coupling efficiency obtained is 95% and for a simulated-plasma loaded coupler this value is in the range of 80%, depending upon the plasma load. If it is assumed that the effects of the high neutron flux present in a reactor environment on the dielectric strength of water are negligible (or eliminated), and that the dielectric breakdown strength of water is approximately 3 kV/cm at nearly 80% coupling efficiency, the power handling capability of the water-filled coupler is estimated to be in the range of 3-6 MW.<>